1. Field of the Invention
The present invention relates to an apparatus, generally called head parts, for rotatably fitting a fork stem in a head tube of a bicycle. This apparatus comprises a first race element fitted on the fork stem, a second race element inserted into an annular space formed between the fork stem and head tube to be opposed to the first race element, and balls arranged between the first and second race elements.
2. Description of the Related Art
In conventional head parts, as shown in FIG. 5, a first race element 1 and a second race element 2 define ball supporting surfaces 1a and 2a, respectively, for supporting balls 6 to perform a bearing function.
With such a conventional construction, a head structure may be formed by the ball supporting surfaces of the first and second race elements and balls assembled together with inadequate precision, such as with a misalignment between the two ball supporting surfaces. This happens when the individual parts are manufactured or assembled with considerable errors, or errors of these parts accumulate to a large amount. As a result, the entire head part assembly has a low quality and low working efficiency.